This volume consists of the English translations of the letters exchanged between Emil Artin to Helmut Hasse written from 1921 until 1958. The letters are accompanied by extensive comments explaining the mathematical background and giving the information needed for understanding these letters. Most letters deal with class field theory and shed a light on the birth of one of its most profound results: Artin's reciprocity law.

“There is extensive mathematical and biographical commentary accompanying the letters, making it possible to follow the discussion without having to be familiar with class field theory and its history. … For anyone interested in the history of number theory in the 20th century, this book is a must-have.” (Fernando Q. Gouvêa, MAA Reviews, July, 2014)